Computer Programming 1 Lab

2020-10-29

Chang, Chi-Hung

Outline

  • OJ-CLI
  • Array
    • Sort Array
    • Search in Array
  • Pointer
  • const
  • Exercise 6

OJ-CLI

OJ-CLI

Installation

  • Ghost Server
    echo 'export PATH="~f103207425/.local/bin:$PATH"' >> ~/.profile
source ~/.bashrc
  • Install from Source Code
    1. Clone this project
      git clone https://github.com/josix/oj-cli.git
    2. Update HOST variable value in file oj-cli/constants.py to the OnlineJudge URL you accessing
    3. Update Shebang(#!/opt/csw/bin/python2.7) value to a suitable one in oj.py

OJ-CLI

Commands

  • oj login
    • Use oj login to login to the account in OnlineJudge. It required you to enter your account information so that oj-cli could access OnlineJudge service successfully. After entering your username and password. oj-cli will respond if you login successfully or not.
    $ oj login
Username:
Password:

OJ-CLI

Commands

  • oj get_assign <assign_no>
    • Use oj get_assign <assign_no> to download the latest assignment from contest. The downloaded files are stored in folder hwX or exX. The folder includes testing data, output data, and template C script, which are named as 1.in, 1.out, and hwX.c(or exX.c) separately.
    $ oj get_assign hw2
$ oj get_assign ex2

OJ-CLI

Commands

  • oj submit <assign_no> <code_file>
    • Use oj submit <assign_no> <code_file> to submit your code to contest.
    $ oj submit hw2 hw2.c
$ oj submit ex3 ../ex3.c

Array

  • Sort Array
  • Search in Aray

Array

  • Sort Array
    Bubble sort
    int SIZE = 5;
int array[SIZE] = {2, 3, 5, 1, 4};
for(int i = 0 ; i < SIZE - 1 ; i++){
    for(int j = 0 ; j < SIZE - i - 1 ; j++){
        if(array[j] > array[j+1]){
            int temp = array[j];
            array[j] = array[j+1];
            array[j+1] = temp;
        }
    }
}

Array

  • Search in Array
    • Linear search
      int SIZE = 5;
int array[SIZE] = {2, 3, 5, 1, 4};
int target = 4;
for(int i = 0 ; i < SIZE ; i++){
    if(array[i] == target){
        printf("index = %d\n", i);
        break;
    }
}

Array

  • Search in Array
    • Binary search
      int binarySearch(const int array[], int target, int low, int high){
    int middle;
    while(low <= high){
        middle = (low + high) / 2;
        if(target == array[middle]){
            return middle;
        }
        else if(target < array[middle]){
            high = middle - 1;
        }
        else{
            low = middle + 1;
        }
    }
    return -1;
}
  • Search in Array

    • Binary search

      int SIZE = 8;
int array[SIZE] = {1, 2, 3, 4, 5, 6, 7, 8};
int target = 7;
printf("%d\n", binarySearch(array, target, 0, SIZE-1);  // 6
      STEP ---1--- ---2--- ---3--- ---4--- ---5--- ---6--- ---7--- ---8---
      (1) L H
      (M)
      (2) L H
      (M)
      (3) L H
      (M)

Pointer

Pointer

void main(){
    int a = 1;
    int b = 2;
    int c = 3;
}
Memory Address Value Variable
0X0012FF70 1 a
0X0012FF74 2 b
0X0012FF78 3 c

Pointer

  • *
    1. Pointer (指標)
      Declare that the type of the variable is a pointer. →\rightarrow It stores address.
    2. Dereference operator (取值運算子)
      Apart from variable declaration, we use * to get the value which is stored in the variable's address.
  • &
    Address-of operator (取址運算子) →\rightarrow Get the variable's memory address.

Pointer

void main(){
    int a = 1;
    int* ptr = &a;  // Declare a int pointer named "ptr" and it points to a's address
Memory Address Value Variable
0X0012FF70 1 a
0X0012FF74 0X0012FF70 ptr
  • Pointer variable: a variable that stores pointer
  • Pointer: point to a variable's address

const

const

  • int* ptr;
    • 指標指的位址可以被改變
    • 所指位址的值可以被改變
  • int* const ptr;
    • 指標指的位址不能被改變
    • 所指位址的值可以被改變
  • const int* ptr;
    • 指標指的位址可以被改變
    • 所指位址的值不能被改變
  • const int* const ptr;
    • 指標指的位址不能被改變
    • 所指位址的值不能被改變

Exercise 6

Matrix Multiplication

[58−469−547−2]×[2−31]=[−18−20−15]\begin{bmatrix} 5 & 8 & -4 \\ 6 & 9 & -5 \\ 4 & 7 & -2 \\ \end{bmatrix} \times \begin{bmatrix} 2 \\ -3 \\ 1 \\ \end{bmatrix} = \begin{bmatrix} -18 \\ -20 \\ -15 \\ \end{bmatrix}

  • Input: Pairs of matrices we want to multiple until end-of-file. Each pair has two matrices.
  • Output: Print the multiplied matrices, or print "Invalid calculation!!" if two matrices cannot be multiplied.

Get repository on Ghost: oj get_assign ex6
Submit on Ghost: oj submit ex6 <code_file>
(Remember to login first!!)

Any Questions?